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1 Connective Tissue Part-2 Dr. Heba Kalbouneh Assistant Professor of Anatomy and Histology

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1

Connective Tissue

Part-2

Dr. Heba Kalbouneh

Assistant Professor of Anatomy and Histology

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Composed of cells, fibers and extracellular matrix.

Highly vascular

Variable regenerative power

Originates from the mesenchyme

Features

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Functions of Connective Tissue

Support

Defense and protection

Storage

Transport

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Extracellular Matrix

Extracellular Matrix = ground substance + fibers

Resists compression and stretching forces.

The water content allows rapid exchange of

metabolites.

Ground Substance

Composed of:

• Glycosaminoglycans:

• Sulfated: keratan sulfate, chondroitin sulfate, dermatan sulfate and heparin.

• Non-sulfated: hylauronic acid

• Proteoglycans: Responsible for the gel state of the extracellular matrix.

• Adhesive glycoproteins: laminin, chondronectin, osteonectin and fibronectin.

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Proteoglycan

Glycoprotein

GAG

Protein core

8hyaluronidase

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Functions of Proteoglycans

Resistance of compression

Retardation of movement of microorganisms

Act as a filter

Types of GAGs

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DistributionGAG

Most connective tissue, cartilage,

dermis, synovial fluid.

Hyaluronic acid

Cartilage, cornea, intervertebral

disc.

Keratan sulfate

Blood vessels, lung, basal laminaHeparan sulfate

Cartilage, bone, blood vesselsChondroitin 4-sulfate

Cartilage, blood vessels, umbilical

cord.

Chondroitin 6-sulfate

Skin, heart valves, blood vesselsDermatan sulfate

Mast cell granules, basophils, liver

lung, skin.

Heparan sulfate (Heparin)

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Connective Tissue Fibers

Collagen

Elastic

Reticular

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Gives the extracellular matrix strength to resist tensile forces.

Formed of protein collagen (30% of all proteins of the body).

H & E: long, wavy pink bundles.

Birefringent

E.M: cross banding at 67 nm.

Fibres are formed of aggregation of fibrils.

Fibrils are formed of tropocollagen.

Tropocollagen is formed of 3 helical polypeptide chains.

Collagen Fibers

α-chains possess 1000 amino acids.

Every 3rd amino acid is glycine.

Other amino acids: proline, hydroxyproline, hydroxylysine.

The sequence of aminoacids determines the type of collagen.

There are 28 types of collagen.

LocationFunctionSynthesizing cellType

Dermis, tendons,

ligament, capsules,

bone, dentin,

cementum

Resist tensionFibroblast, osteoblast,

odontoblast, cementoblast

I

Hyaline and elastic

cartilage

Resists pressurechondroblastsII

Reticuloendothelial

system, lung, skin

Form structural

framework of organs

Fibroblasts, reticular cells,

smooth muscle, hepatocytes

III

Basal laminaMeshwork of the

lamina densa

Epithelium, muscle,

Schwann cells

IV

As in type I and

placenta

Associated with type

I.

Fibroblasts, mesenchymal

cells

V

Derma-epidermal

junction

Anchoring fibrils

between the lamina

densa and reticularis

Epidermal cellsVII

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Major Types of Collagen

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16

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Collagen bundle

Fibers

Fibrils

Tropocollagen

3 Helical polypeptide chains, α-chains.

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EXTRA CELLULAR

Cleavage and assembly

Intracellular* Transcription (Nucleus).

* Translation (rER).

* Hydroxylation (rER).

* Glycosylation (rER & Golgi).

* Formation of the triple helix.

* Secretion of procollagen (trans Golgi network

and microtubules).

*** Vit. C is essential

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Vitamin C deficiency (Scurvy)

Keloid

Ehlers–Danlos syndrome

Clinical application

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Keloids

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Elasticity is due to elastin.

Stability is due to fibrillin microfibrils

(resistant to boiling).

Appears yellow in fresh tissue (if large

amount is present)

Digested by pancreatic enzyme elastase

Elastic fibers

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Elastic fibers consist of individual microfibrils(fibrillin) which are

embedded in an amorphous matrix (90% of the fiber and composed of

elastin)

Elastic material is found in certain ligaments (elastic ligaments), some

cartilage (called elastic cartilage) and in large arteries (elastic arteries).

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Elastin molecules are crosslinked by desmosine

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Consist mainly of type III collagen.

Short, thin and branching.

High sugar content

Give PAS +ve reaction.

Stain with Silver Nitrate (Argyrophylic).

Found mainly in reticular lamina of basement membrane, RES

organs (supporting stroma)

Reticular fibers

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Reticuloendothelial System: liver, spleen, lymph nodes and bone marrow

Connective Tissue Fibers

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Fiber Properties

Collagen Undulating course of longitudinally striated

bundles, stain pink-red in H&E. Nonextensible.

Elastic Forms sheets or lamina, Unstained in H & E.

Reversibly extensible. Stains brown-black in

Orcein or Resorscin Fuchsin.

Reticular Delicate network, Unstained in H & E. Reversibly

extensible. PAS +ve, stains black in AgNO3

(Argyrophilic).

Classification of Connective Tissue

• Connective tissue proper: dense and loose• Loose (areolar)• Dense regular• Dense irregular

• Special connective tissue:• Reticular• Elastic• Adipose• Bone• Cartilage • Blood

• Embryonic connective tissue• Mesenchymal connective tissue• Mucous connective tissue

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Loose connective tissue

• Called also areolar connective tissue

• Typically contains cells, fibers and ground substance in equal amounts

• Supports epithelium (ex. lamina propria)

• Surrounds small blood vessels

• Fills spaces between muscle and nerve cells

• Its flexible but not very resistant to stress

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Dense irregular connective tissue

• Bundles of collagen fibers are randomly interwoven with no

definite orientation

• Provides resistance to stress from all directions

• Dermis of skin (deeper layer), organ capsules, submucosa

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Dense regular connective tissue

• Parallel Bundles of collagen fibers with few fibrocytes aligned with

collagen and separated by very little ground substance

• Provides resistance to prolonged or repeated stresses exerted in the same

direction

• Ligaments , tendons, aponeuroses

• Tendons are poorly vascularized and repair of damaged tendons is very

slow

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Tendon

(collagen)

Collagen

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Reticular connective tissue

• Consists of reticular cells (modified fibroblasts) and the

network of reticular fibers formed by them

• Forms the structural framework in which the cells of the organ

are suspended

• In the liver, bone marrow, lymph nodes and the spleen

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Mesenchymal connective tissue

• Mesenchyme forms the undifferentiated "filling" of the early embryo.

• It consists of mesenchymal cells, which interconnect by slender cell processes.

• Mesenchymal cells have stem cell properties, i.e. they are able give rise to other cell and tissues types.

• The wide extracellular space between the mesenchymal cells is occupied by ground substance, which can be stained with dyes that also stain mucin - hence the alternative name of this tissue type: mucoid connective tissue

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Mesenchymal connective tissue

Mucoid connective tissue also forms a compliant cushion around the

vessels of the umbilical cord, where it is also called Wharton's jelly.

In adult humans, mesenchymal connective tissue is only found in the

dental pulp.